Method for processing poultry shell eggs

ABSTRACT

Time at temperature methods of treating whole eggs which make them safer to eat without affecting the functionality or organoleptic properties of the eggs. The keeping quality of the eggs is also improved.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/156,273 filedNov. 22, 1993, now U.S. Pat. No. 5,589,211. The '273 application is acontinuation-in-part of U.S. application Ser. No. 07/746,940 filed Aug.19, 1991, now U.S. Pat. No. 5,431,939. The '940 application is acontinuation-in-part of U.S. application Ser. No. 07/674,495 filed March25, 1991, now U.S. Pat. No. 5,283,072 which was a continuation of U.S.application No. Ser. 07/349,974 filed May 8, 1989, and abandoned, whichwas a continuation of U.S. application Ser. No. 07/196,878 filed May 19,1988, and abandoned, which was a continuation of U.S. application Ser.No. 07/070,597 filed Jul. 8, 1987, and abandoned, which was acontinuation of U.S. application Ser. No. 06/758,086 filed Jun. 24,1985, and abandoned.

TECHNICAL FIELD OF THE OF THE INVENTION

The present invention relates to poultry shell eggs of overall improvedfood safety quality and to shell egg pasteurization methods with timeand temperature process parameters equivalent to or exceeding thoseminimum standards established by the United States Department ofAgriculture (USDA) for hole liquid eggs.

DEFINITIONS

Functionality or Functional Properties: eggs contribute to the volume,structure, texture, and keeping quality of baked products. Thecoagulation of egg proteins during heating brings about the thickeningof custards and pie fillings and the binding of pieces of food togetheras in loaves or croquettes. When eggs are whipped, the proteins formelastic films and incorporate air that provides the leavening and volumeneeded in such products as angel food cakes, souffles, sponge cakes, andmeringues. The foam structure of these products is made rigid bycoagulation of the protein during baking. The elasticity of egg proteinfilms is also important in popovers and cream puffs; the protein filmsstretch when steam is produced during baking and later coagulate to formthe framework of the product. Lipoproteins of the yolk are goodemulsifying agents. They make it possible to disperse the oil in theother ingredients and thereby contribute to the consistency ofmayonnaise and salad dressings and the structure of cream puff shells.

Whole eggs are used in sponge and layer cakes, bread, and rolls. Yolksare used in mayonnaise and salad dressing, sweet goods, doughnuts, andcakes in which more yellow color is desired. Whites are used in angelfood cakes, meringue toppings, puff pastry, white pound cakes, layercakes, cupcakes, certain candies, and a number of premixed products.

The extent to which the functional properties are affected bypasteurization is determined by testing the performance of the eggsunder conditions in which damage is readily observed.

Pasteurization (or Pasteurization Process) Temperature: The temperatureat which a pasteurization medium (air or other gas, water, oil, or otherfluid, etc.) is maintained for an RPT such that a destruction of anyinfections present in an egg at least equal to that obtained byobserving the minimum or protracted standards mandated by the USDA forliquid whole eggs is obtained on the shell of the egg and throughout andin the furtherest reaches of the egg interior including the egg yolk.Pasteurization temperatures range from 130° F. to a temperatureapproaching but less than 140° F. (<140° F.).

EqT: The point at which all particles throughout the mass of a shell eggreach equilibrium with the selected pasteurization medium temperatureand the point at which RPT begins. EqT time is the time required toobtain EqT of an egg.

Real Process Time (RPT): That part of the TPT after all particlesthroughout the mass of a shell egg have reached a selectedpasteurization temperature enabling the meeting of the U.S. Departmentof Agriculture standards for liquid whole eggs.

Total Process Time (TPT): That total length of time for which an egg isheated beginning with the egg at an initial preprocessing temperatureand ending when the application of heat to the egg is terminated. TPTequals EqT time plus RPT.

Throughout the mass of an egg: encompasses all matter in the shell of anegg and within the shell.

Temperatures are often expressed hereinafter in the form xxx to yyy° F.(±z° F.). This is to be interpreted as a temperature range in which thelower limit is a nominal xxx° F. with a tolerance of ±z° F. and theupper limit is a nominal yyy° F. with a tolerance of ±z° F.

BACKGROUND OF THE INVENTION

For many years minimum food safety processing standards for variouscommodities have been promulgated and enforced by the United StateDepartment of Agriculture. While long enforced for liquid whole eggs andegg products of a wide variety, based upon minimum standards ofpasteurization processing, food safety standards have never beenestablished for shell eggs. Indeed, as a review of the prior artidentified in this specification has shown, there has not heretoforeeven been available technology for successfully pasteurizing shell eggsto acceptable standards, that is, to standards equaling USDA guide-linesestablished for the other egg products mentioned above.

Shell eggs are an important commodity affording the consumer manynutritional advantages unparalleled by any other food product. Theseadvantages include very favorable costs per nutritional unit of foodvalue, convenience of preparation, gastronomic enjoyability, culinaryusefulness, and availability.

It has long been known that some shell eggs contain infectious organismssuch as Salmonella which, from a food safety standpoint, is of primaryconcern. Techniques for improving the food safety of shell eggs bydestroying these infectious microorganisms have been proposed. However,aside from those effective for external sanitation, none are known tohave ever been successfully employed. Instead, processing, handling, andother aspects of egg production have been emphasized in an effort toindirectly reduce the magnitude of the problem.

Awareness and concerns regarding infectious organisms in the yolk of ashell egg have been slow in developing. Both awareness and concerns havebeen amplified increasingly over the past decade as a result of numerousoutbreaks of food poisoning irrefutably attributable to suchyolk-associated organisms.

Advanced social programs and medical care have made a vastly enlargedpercentage of the population dramatically more vulnerable to toxiceffects of such food borne infections. At increased peril are thosesignificant segments of the population of increased longevity or thosewho are immunocompromised due to organ transplants, immunosuppressiontherapies, and diseases caused by or causing compromised immune systemssuch as AIDS.

Increasingly, concerns over the safety of eggs consumed as a foodilluminate the issue of transovarian infection developed deep inside theegg as it is formed in the oviduct. In addition, infectious organismsare known to penetrate the pores of shells and perhaps even thevitelline membranes of eggs, contaminating deeper proteins including theyolks. Also, for reasons not entirely clear, diseased hens are now knownto excrete microorganisms inside the egg. The offending microorganismcurrently identified with this problem is Salmonella enteritis (S.enteritis).

Salmonella are small, gram negative, non-sporing rods. They areindistinguishable from Escheichia coli (E. coli) under the microscope oron ordinary nutrient media. All species and strains are currentlypresumed to be pathogenic for man.

As a disease organism, Salmonella produces a variety of illnessesdepending on the species. S. typhimurium, which translates to"Salmonella from Typhus Mary", needs no other explanation. S. typhicauses enteric fever. S. paratyphi type A and type B cause a syndromewhich is similar to but milder than typhus.

Reported cases of severe gastroenteritis (stomach flu) have implicatedS. bareilly, S. newport, and S. pullorum as well. The mortality range isprimarily based on the victim's age and general health. S. choleraesuishas the highest reported mortality rate at 21%.

S. senftenberg is reputedly the most heat resistant specie ofSalmonella. It is reportedly destroyed at 130° F. (54.4 °C.) after 2.5minutes. It is estimated that S. senftenberg 775W is 30 times more heatresistant than S. typhimurium. Turkeys (10 to 11 lbs.) inoculated with115,000,000 microorganisms of S. pullorum required holding at an averageinternal temperature of 160° F. (71.1° C.) for four hours and 55 minutesbefore the bacteria were destroyed.

Over 2,000 other species of Salmonella are known. The number increasesyearly.

Among the most common vehicles for food poisoning caused by Salmonellaare eggs. Widespread publicity on illnesses and deaths attributed tocontaminated eggs containing S. enteritis in Europe over the past fewyears has reportedly resulted in a reduction in egg consumption. In somedistinct marketing areas the reduction has been estimated to be as greatas 50 percent. The problem is being perceived in Europe and in theUnited States as chronic, spreading, and a major public healthchallenge. Nevertheless, in the United States alone, approximately240,000,000 dozen eggs are still consumed annually.

A recent article in the Nutrition Action Health Letter published by theCenter for Science in the Public Interest (July/August 1991 edition,Volume 18, number 6, "NAME YOUR (FOOD) POISON") relates a current trendof growing concern. The article reports that, according to governmentestimates, 80,000,000 cases of food poisoning yearly result in about9,000 deaths and several billions of dollars in health costs.

The article claims that the primary causative foods are, in order: dairyproducts, eggs, poultry, red meat, and seafood.

The article reports that 1 in 10,000 eggs is contaminated withSalmonella enteritis. The average American consumes about 200 eggs peryear. If your egg consumption is average, your chance of downing an eggcontaminated with one or more species of Salmonella is 1 in 50; or, putanother way, it is likely that you will eat four contaminated eggs thisyear.

If you are over 65 or have a disease such as cancer or AIDS associatedwith a weakened immune system, the article advises: don't eat raw eggs;don't drink egg nog; don't eat Caesar salads, home made mayonnaise, icecream, or "health" drinks that call for raw eggs. Cook all eggsthoroughly--solid white and yolk.

Compounding the contamination problem is the improper handling of eggsin institutional and even home settings. Often cited is the all toofrequent observation of eggs setting out at room temperature for longperiods of time in institutional kitchens. Such unknowledgeabletreatment promotes bacterial advancement in even the freshest egg.

Little is known about virology inside the egg. It has long been and isstill believed by some that shell eggs are sterile inside the shell.Needle puncture samples of the inside of an egg including both yolk andwhite taken under aseptic conditions usually do demonstrate a negativeplate count when cultured. Nevertheless, it is well known that, wheneggs are broken in quantity, they immediately demonstrate significantgross populations of infectious microorganisms. It is not unusual tofind plate counts ranging from several hundred to many thousands, evenwhen the surface of the egg shells have been cleaned of filth and washedin the best antiseptics known to food science. The occurrence of S.enteritis inside the shell egg is now also well documented.

One source of infection arises from the fact that egg shells havenumerous pores which permit the egg to breathe. Pore holes vary in size.When the egg is laid, those holes come into contact with organic refusein the cage. It is very likely that some microbes contacting the egg areof a size which allows them to fit through the pores. Once inside, themicrobes are not uniformly spread around the interior of the egg but areretained in small patches on the inner shell membrane, which has yetsmaller pores than the shell.

Washing actually spreads microbes more evenly, increasing contaminationthrough greater surface contact with entry pores in the egg shell. Whenthe eggs are cracked, the shell membranes may be ripped and torn loose.And, when the shells are subsequently emptied, the eggs may be pepperedwith this stored inoculum in addition to airborne bacteria.

Also, as egg temperatures vary, there is active and ongoing gas andvapor exchange between the yolk and white via the vitelline membrane,between the white and the inside of the shell via the outer and innershell membranes, and also between the shell and the outside environment.Airborne microorganisms can also reach the interior of the egg throughthese mechanisms.

Finally, as discussed above, eggs can be, and frequently are,contaminated by transovarian infection. The extent of this problem isstill not known. Thus, an egg may be unsafe to eat even if there is notransport of harmful microorganisms from the exterior of the egg to itsinterior. Worse yet is when both of the egg infecting mechanisms--porepenetration and transovarian infection--are at work.

U.S. Pat. No. 4,808,425 issued Feb. 28, 1989 to Swartzel et al.elaborates on the USDA stanards for pasteurizing liquid eggs, summarizesthe disclosures of many references, identifies resources relative to eggpasteurization, and adequately points out many of the problemsassociated with available techniques for making liquid but not shelleggs of safer food quality. Swartzel et al. employ a conventionalpasteurization technique--time at temperature--to treat liquid eggproducts. The products are contacted against a heated surface at hightemperatures; i.e., above 140° F. (60° C.) for short durations of lessthan 10 minutes. This approach is not applicable to a shell egg.

The minimum time at temperature processing mandated by USDA standardsproduces liquid eggs which are safe to eat because all particles havebeen exposed to RPT; and, if the liquid eggs are carefully processed, anat least acceptable degree of functionality and other valued propertiescan be retained. Standards for shell eggs are lacking because, up tonow, a reliable time at temperature technique for making shell eggs safeto eat has not existed. In particular, there is not known to exist anyeffective process which can be employed to process whole eggs to thestandards mandated for liquid eggs; i.e., to ensure that all particlesthroughout the mass of the egg--which includes the shell, the outershell and egg membranes, the albumen layers or egg white, the chalaza,the vitelline membrane, and the yolk to its innermost reaches orcenter--are exposed to appropriate temperatures for times adequate foran acceptable kill of any harmful organisms that might be present.

Other researchers have focused their attention on time and temperaturetreatments for devitalization of vital shell eggs. To a much lesserextent, pasteurization of shell eggs to improve food safety quality hasbeen considered.

Funk (Stabilizing Quality in Shell Eggs, Missouri AgriculturalExperimental Station, Research Bulletin no. 362 and Maintenance ofQuality in Shell Eggs by Thermostabilization, Missouri AgriculturalExperimental Station, Bulletin no. 467) and Murphy and Sutton(Pasteurization of Shell Eggs to Prevent Storage Rot and MaintainQuality--a Progress Report of Experimental Work, Misc. Publication no.3317, Department of Agriculture, New South Wales, Australia) purportedto preserve shell eggs by briefly heating the eggs for 15 or 16 minutesat temperatures ranging from 130 to 135.9° F. (54.4° C. to 57.7° C.) andfrom 129.2 to 136.4° F. (54° C. to 58° C.). Irrespective of the startingtemperature of the shell egg to be processed, these prior art processescannot possibly provide a Salmonella free or Salmonella reduced inneregg. Neither can they achieve equivalents of the minimum requirementsestablished by the USDA for processing liquid whole eggs.

The growth of external food poisoning infections are in some of theTPT/temperature ranges provided favorably influenced in the outermostlayers of the shell egg. In many other ranges, external food poisoninginfections will be significantly worsened. In all cases, temperaturesnear and at the egg yolk center never achieve the minimum temperatureneeded for a time effective to kill significant concentrations ofinfectious microorganisms.

On the contrary, because the internal temperatures reached near or inthe center of the yolk are not high enough to destroy Salmonella andother infectious microorganisms, these prior art techniques,irrespective of how employed or combined, cannot meet accepted minimumstandards for other egg products and by and large can only attaintemperatures in the yolk within the times suggested which are in a rangethat will cause substantial increases of any food poisoning infectionspresent therein. Within a very narrow range of those parameters,processed eggs may or may not become more infected. In all otherinstances a shell egg carrying a minor, non-lethal infection in the yolkcan by use of such methods deteriorate markedly and become a verysignificant health risk, if not a toxic food.

In his U.S. Pat. No. 2,423,23 issued 1 Jul. 1947, Funk is concernedprincipally with "sterilizing or devitalizing" embryos in vital shelleggs. Confusingly, Funk ambiguously and interchangeably uses the termsterilization, stabilization, devitalization, and pasteurization indescribing this objective. Funk claims that poultry eggs can bepasteurized, stabilized, and devitalized of embryonic life by immersingfreshly laid, room temperature eggs in oil or water at temperaturesranging from 110° F. to 145° F. (43.3° C. to 62.8° C.) for times rangingfrom five to forty minutes or presumably, in the alternative, from 110°F. to 145° F. for from forty to five minutes.

Funk did not account for the fact that infectious microorganisms such asSalmonella are to be found throughout and in any or all specific partsof an egg, such as the yolk, whites, and membranes and even at thecenter of the yolk. Funk is principally concerned with devitiating theshell egg embryo and only with "destroying bacteriological organismswhich may have penetrated the egg shell and . . . extended even so faras the yolk . . . . " He did not disclose in his patent or take intoaccount the fact that the time required for processing a shell egg tomake it safe to eat at specified temperatures is one thing for theouter, non-yolk portion of a shell egg and quite another for the centerof the yolk. The result is that most of the process conditions claimedby Funk only result in conditions which at best can not meaningfullyimprove any preexisting infectious condition and at worst are certain tosignificantly increase health hazards from food poisoning infections. Asapplied to a shell egg, Funk cannot achieve even the minimum USDAprocessing standards (see FIG. 2) for liquid egg products. Use of othertime/temperature combinations embraced by the broad statements in theFunk patent (which also cannot meet the minimum processing standardsreferred to above) result in the whites of the eggs being visibly cooked(see FIG. 8).

The Funk process parameters are temperature and TPT. As defined above,this is the total time a shell egg is held in a pasteurization mediumheated to a selected pasteurization process temperature. This is quitedifferent from the critical RPT, which is that portion of TPT in whichall particles throughout the mass of the egg including those at thecenter of the yolk are at an effective pasteurization temperaturemeasured from the point at which EqT is reached. There is no evidencethat Funk recognized or appreciated the criticality of the differencebetween TPT and RPT. Even if he had, he presumably would not have madethis distinction because, for purposes of devitiating an egg embryo, TPTand RPT are one and the same; i.e., there is little or no differencebetween these two process temperature conditions in pasteurizing,devitalizing, and sterilizing whole eggs to retard spoilage by makingviable eggs infertile; i.e., by preventing ongoing embryonicdevelopment.

Lethal thermal damage to any part of an embryo, even only at itssurface, is adequate for this purpose. Unlike the embryos in vital eggs,infections are composed of a multitude of micro-entities. Lethal damageat some point to a portion of this multifarious milieu is not adequateto destroy the infection as is the case with an embryo which may bekilled if even a small part is heated to a high enough temperature. Tobe effective against infections frequently scattered throughout asubstrate, the time at temperature must be adequate to kill largenumbers of infectious organisms at these widely scattered locations. Ina shell egg, that means that the pasteurization temperature must bereached and maintained for the necessary time throughout all parts ofthe egg containing the microorganisms. In this case, TPT and RPT aredistinct; the distinction becomes increasingly critical as that mass ofthe egg which is potentially infectable is increased.

Funk's statement of process parameters for the devitalization of an eggembraces many time and temperature combinations which may be effectiveto achieve that object. However, when employed to kill food borneinfections, those time and temperature combinations which apply toembryonic devitiation cannot adequately kill Salmonella or other harmfulbacteria commonly found in eggs for reasons just discussed. Theunfortunate fact is that most of those time/temperature combinationsembraced in Funk can only significantly increase contamination insidethe egg because they for the most part result in the egg being underconditions near to or optimal for maximum bacterial growth. An exampleis Funk's own preferred pasteurization parameters--five to ten minutesTPT at 138° F. (58.8° C.) and twenty to forty minutes TPT at 130° F.(54.4° C.).

Funk's preferred "pasteurization" method for a shell egg never achievesany RPT at the yolk but does achieve active growth range conditionsthere over a significant period of time. If the initial temperature ofthe shell egg is significantly lower than 70° F., as is or should alwaysbe the case in real world processing, Funk's preferred conditions willmore seriously fail, resulting in dramatically favored conditions likelyto increase any food poisoning infection present in the yolk.

Funk's preferred "pasteurization" process times and temperatures are notthe worst cases suggested to one of ordinary skill in the art by hispatent. Indeed, when many, if not most, of the Funk times andtemperatures provided for pasteurization, sterilization, anddevitalization of vital egg embryos are applied to the "pasteurization"of shell eggs to improve food safety quality, the results as confirmedby tests always fall short of and are often contrary to that objective.Moreover, as measured at the yolk, eggs processed pursuant to the mostfavorable possible conditions specified by Funk cannot meet the processstandards provided in the USDA Protracted Whole Egg Standard for LiquidWhole Eggs (see FIG. 1) or even the minimum standards mandated by theUSDA for liquid whole eggs (see FIG. 2).

For example, take a shell egg infected superficially at the inner shellsurface (not uncommon) and also in the yolk (estimated to occur in 1 outof every 10,000 eggs). Pasteurize that egg according to Funk'sspecifications: from 40 minutes at 110° F. to 5 minutes at 140° F. Atthe lower temperature/longer time--40 minutes at 110° F.--thesuperficial temperatures even at the inner surface of the shell can beexpected to promote the growth of bacteria and result in substantialworsening of any food poisoning infections present. Those temperaturesachieved near or at the yolk center could reach but would never exceedthe optimal growth conditions for food poisoning infections ofSalmonella. The result, if infections were present, could easily becatastrophic increases in food poisoning concentrations. At shortertimes and higher temperatures such as 134-136° F., the temperature of aninfected yolk center would never exceed about 125° F., yielding onlyeggs with increased food poisoning potential.

If the above-discussed time/temperature relationships are reversed--5minutes at 110° F. to 40 minutes at 140° F.--as is equally reasonablefrom Funk's claim 1 and other statements in his patent, the lowtemperature/short time relationships constitute what could reasonably beselected as optimal by a bacteriologist to best culture Salmonella ineggs as a growth medium. At the other end of the spectrum--the extremehigh temperature/long time combination of 140° F. for 40 minutes--, the"pasteurized" eggs would be "hard-boiled" in at least the exteriorlayers. All inbetween permutations of Funk conditions are ineffectual atbest to meet even the minimum processing conditions required by the USDAfor liquid whole eggs as shown in FIG. 2.

At the same time, even starting with shell eggs already at 70° F., letalone at more realistic, lower, cold storage temperatures, shell eggsprocessed according to Funk in the near extreme regime (>139° F./39.2 to40 minutes TPT) will never achieve the RPT near or at the egg centerneeded to meet the basic protracted USDA temperature/time regimes forliquid whole eggs. To make matters worse, when shell eggs areimmediately immersed into liquid at extreme temperature differentials(greater than about 65° F.-70° F.) as they could well be in followingFunk's teachings, a significant number will crack. Cracked eggs are aloss. They are difficult to handle, unmarketable to consumers and otherpurchasers of whole eggs, and exceptionally susceptible tocontamination.

In short, by even the most generous interpretation, no obviouscombination of Funk's sterilization, devitalization, or pasteurizationtemperatures and times (from 110° F. to 140° F. for 5 to 40 minutes orfrom 110° F. to 140° F. for 40 to 5 minutes) can achieve even theminimum, FIG. 2 USDA process standard for liquid whole eggs without"cooking" at least the egg whites to some extent; and this isunacceptable because of consumer rejection and resulting loss offunctionality. It is more likely, because it is true in the largemajority of the available time/temperature combinations, that the Funkprocess would, if the egg being processed is infected at the yolk and/orsuperficially on the shell's inner surface, increase rather thandecrease, perhaps dramatically, any food poisoning hazard present. Theprocess would surely promote the growth of or at best substantiallyleave unaffected any harmful microorganisms present in the egg.

Application of the Funk process to eggs almost certainly results in eggsdependably rid of a living embryo. But with respect to pasteurizationdesigned to improve food safety of shell eggs and with the questionableexception of a few time and temperature combinations effective to reducesuperficial inner shell infections, Funk's process is only likely toproduce infected shell eggs which remain or are made more hazardous toconsumers and/or which are visibly partially cooked at the outer layers.

New serotypes of infectious organisms continue to develop. Increasedproduction, mass handling, and widespread distribution of food productscontinue to increase the risks of food poisoning. Food poisoningincidents related to eggs are not uncommon and may even be increasing.Almost all food products have well developed standards of processing forensuring food safety. With respect to eggs and egg products, only shelleggs have no standards for pasteurization. The primary reason for thislack of food safety pasteurization standards as required for all otheregg products is undoubtedly attributable to the lack of knowledge of anefficacious process for making shell eggs safer to eat. In practice,known processes such as the one discussed above and proposed by Funk areinefficacious and either fail completely to achieve any meaningfulbenefits or are highly likely if not certain to result in products withsubstantially increased health hazards from food poisoning.

SUMMARY OF THE INVENTION

Now discovered and disclosed herein are novel, practical methods fortemperature and time pasteurization of a shell egg throughout its entiremass with a degree of effectiveness equaling or even exceeding thatobtained by employing the USDA minimum and protracted standards forliquid whole eggs, thereby reducing to an acceptable level thepossibility that the subsequent ingestion of the processed egg mightcause food poisoning, typically an illness consisting of gastroenteritisand fever lasting for several days but a deadly threat if a person inone of the susceptible categories identified above is infected. At thesame time, these novel shell egg pasteurization techniques do not undulycompromise the integrity, functionality, or quality of the egg.

Process temperatures capable of producing this significant advantage forcommercial size eggs (54 to 68 grams) with an initial,pre-pasteurization temperature of 45° F. or higher are those in therange of from about 130° F. to near, but less than, 140° F. Temperaturessubstantially above 139° F. are not useful because: (1) the egg will intoo many instances crack upon being subjected to pasteurization, and/or(2) whites will begin to visibly cook before the egg yolk pasteurizationtemperature at the center of the egg yolk has been achieved, let alonemaintained long enough to meet pasteurization standards equivalent tothose mandated by the USDA for liquid eggs. At temperatures below thespecified minimum, Salmonella and other harmful microorganisms includingmolds, other bacteria, and even viruses are not effectively killed andmay even thrive.

Process times employed at the temperatures just identified in the novelpasteurization processes disclosed herein to meet minimum requirementsequivalent to those mandated by the USDA for liquid eggs range from aminimum RPT of about 50 minutes at 130° F. to a minimum RPT of about4.50 minutes at 139.5° F. The time/temperature parameters taken intoaccount include these factors: (1) the temperatures achieved by allparticles in and throughout the mass of a shell egg; the time for whichall particles are held at that temperature; and the average time thatevery particle is heated, assuring that each particle is subjected to atleast the minimum conditions needed to guarantee effectivepasteurization; (2) the minimum-to-maximum process parameters which willavoid or minimize adverse changes in appearance and performance vs.maximum kill of infections; and (3) the attainment of conditions neededto provide the equivalent of the minimum USDA mandated pasteurizationstandards for liquid whole eggs.

The initial egg temperature at the beginning of the pasteurizationprocessing of whole shell eggs may range from a low of about 38° F. to ahigh of about 60° F. with a probable average year around temperature ofabout 55° F. The average preprocessing temperature should be somewhatlower than 45° F. for whole shell eggs destined for consumerdistribution.

Effective pasteurization in accord with the principles of the presentinvention requires that the preprocessing starting temperature be known.This temperature is used to determine TPT. As suggested above, TPT hastwo components, EqT time and RPT, with EqT time being the time requiredfor an egg to reach equilibrium with the temperature of thepasteurization medium throughout its mass and especially in its mostthermally inaccessible portions such as the center of the yolk. Onlyafter EqT is achieved can RPT, the time at a selected pasteurizationprocess temperature equivalent to that mandated for liquid whole eggs,begin. Once the center of the shell egg is at the selectedpasteurization temperature, the egg is processed at USDA-mandatedtemperatures and times to ensure time-at-temperature compliance at thecenter of the shell egg yolk with at least the minimum USDA standardsfor liquid whole eggs. This ensures that, completely throughout itsmass, the egg is maintained at a temperature high enough to effect thedestruction of harmful bacteria for a time long enough for that goal tobe realized.

Examination of FIG. 2 shows the following minimum temperature/timerequirements for liquid whole eggs, and those parameters may be appliedequivalently to shell eggs once the selected pasteurization temperaturehas been achieved at the shell egg yolk center. The same data appears intabular form in Table 1. In each instance, the indicated time is theminimum RPT needed for an acceptable or better kill of harmfulmicroorganisms at the corresponding temperature.

                  TABLE 1    ______________________________________    Temperature      Required RPT (min)    ______________________________________    130° F.                (54.4° C.)                         = 65    131° F.                (55.0° C.)                         = 49    132° F.                (55.6° C.)                         = 38    133° F.                (56.1° C.)                         = 28    134° F.                (56.7° C.)                         = 20    135° F.                (57.2° C.)                         = 16    136° F.                (57.8° C.)                         = 11    137° F.                (57.8° C.)                         = 8    138° F.                (58.9° C.)                         = 6    139° F.                (59.4° C.)                           = 4.75    140° F.                (60.0° C.)                          = 3.5    ______________________________________

When the Table 1 pasteurization time and temperatures are applied toshell eggs, additional, EqT time must be allocated from the time the eggis placed in a heat transfer or pasteurization medium maintained at thedesired pasteurization temperature in order for the center of the yolkto achieve EqT--the initial point of RPT and the point at which the eggreaches temperature equilibrium with the heat transfer medium. The RPTfor a given pasteurization regime can only begin after this point hasbeen reached and heat has been transferred through the external portionsof the shell egg into the center of the yolk such that the temperatureat the yolk center and at every other locus throughout the mass of theegg has reached equilibrium with the process medium.

The total time for the entire egg to come to equilibrium with theprocess medium or reach a predetermined effective process temperature,EqT, added to the real processing time, RPT, as set forth in FIGS. 1 and2 and Table 1 equals the total processing time, TPT.

Among factors determining the time required to reach EqT are egg size,the preprocess temperature of the egg, and the selected pasteurizationprocess temperature.

For purposes of achieving heat transfer through the shell to theinterior of an egg, one liquid (oil, water, glycol or the like) willwork about as well as another provided, of course, that the liquids aresafe for this use. A gas such as air, humidified air, or air mixed withgases such as carbon dioxide or nitrogen can be used as a pasteurizationmedium but is not preferred for heating eggs to EqT. Such gases may beused for the RPT phase of the pasteurization process or for TPTprocesses which involve both EqT and RPT phases. However, for RPT steps,liquids are also usually preferred. The just-identified gases arefrequently preferred for tempering, a technique described in detailhereinafter and optionally employed to ensure efficacious pasteurizationof eggs in processes employing the principles of the present invention.

It is not uncommon for eggs in a process lot to be at differenttemperatures. The ignoring of this significant condition can lead to theselection of inappropriate EqT, RPT, and/or TPT time and temperaturecombinations. Those parameters providing effective, if not optimal,pasteurization of eggs at one initial temperature may result in thecooking of the whites of eggs at a higher initial temperature.Conversely, if the process batch contains eggs with a lower initialtemperature, those eggs may not be subjected to the minimum RPT for theselected pasteurization temperature specified in FIG. 2 and Table 1.

Tempering may be employed in accord with the principles of the presentinvention in instances where disparity in initial egg temperatures isevident or even suspected to eliminate the problems the temperaturedisparity may cause. Tempering is an initial or pre-processing step inwhich the eggs are held at a sub-pasteurization temperature long enoughfor the eggs to all come to the same temperature. This promotesuniformity of results in the subsequent pasteurization of the eggs,significantly reducing or even eliminating the likelihood of there beingeggs with cooked whites and/or insufficiently pasteurized eggs at theend of the pasteurization process. Tempering can also be employed toreduce, if not eliminate, thermal shock cracking of the eggs beingprocessed.

Tempering can be carried out in air and other gases. The gas can be dryair or air humidified to prevent evaporative losses of water from theegg during tempering, a phenomenon that is preferably avoided because ofthe weight loss suffered as an egg dries. An alternative, if thepasteurization process medium is not water, is to add water to thatmedium to make up evaporative losses during pasteurization by restoringwater lost from the egg by evaporation.

The shortest effective tempering times are preferred. It is undesirableto hold the egg at any temperature which favors microorganism growth forany longer than necessary; and the tempering temperature might be one ofthat character.

The basic shell egg pasteurization process takes into account processsteps and factors other than those identified above such as: (1) anormal range of egg sizes at any normal ambient preprocess temperature,tempered or untempered, packaged or unpackaged, or coated; (2) liquidand gas or fluid processing; and (3) the use of turbulence or vibrationto promote the transfer of heat into the eggs. The process preferablyemploys primary pasteurization parameters of >134.5° F. to <139.5° F.(±ca. 0.3° F.) for a TPT of from about 23 to about 56 minutes or, formaximum TPT, pasteurization process temperatures of 130.1° F. to 134.6°F. (±about 0.3° F.) for TPT's of from about 46 to about 345 minutes.

Preferred TPT's and pasteurization temperatures for eggs weighingbetween 35 and 90 gms and at a normal preprocess temperature between 40°F. and 70° F. are 138° F.±1.5° F. at 44±about 8 minutes. Preferred TPT'sfor eggs weighing between 50 and 80 gms at preprocess temperaturesbetween 45° F. and 55° F. for pasteurization temperatures of 138°F.±0.75° F. are about 44±5 minutes. These time and/or temperature rangesare modified, using test data and routine trials, when intermittenttemperature pasteurization as described in succeeding paragraphs of thisspecification is employed.

There are important versions of the invention in which heating of theegg is accomplished in stages with one or more of the heating stepsbeing followed by a dwell time in which the temperature equilibratesthroughout the interior of the egg.

Another, somewhat similar approach is pasteurization in stages withsubstantial dwell times between the stages. Tests have demonstrated thatpasteurization within the ranges of time/temperature parametersdescribed above followed by a second pasteurization treatment may besynergistically effective to provide longer shelf lives.

Because of the virtually unlimited number of options this offers, it isimpractical to list the parameters for each and every option.Furthermore, this is unnecessary; the parameters appropriate for aparticular option employing intermittent or discontinuous heating can bereadily and routinely determined because the critical criteria areknown. Specifically, the pasteurization temperature and RPT must be suchthat, at the end of the pasteurization process, all particles throughoutthe mass of the egg will have been heated at the selected pasteurizationtemperature for an RPT equivalent to at least the minimum mandated by aUSDA Standard for liquid whole eggs (FIGS. 1 and 2 and Table 1).

Like pasteurized eggs and egg products, a shell egg processed bytime-at-temperature pasteurization will typically suffer some diminutionof overall sensory properties and some loss of functionality. Generally,in processing shell eggs in accord with the principles of the presentinvention, any quantitative changes resulting from implementation of theinvention under the less extreme process conditions are not noticeableby a consumer of average sensitivity. Under extreme conditions, such aspasteurization at a temperature of 131° F. for 100 to 240 minutes,products which may have some average-consumer-noticeable differences maybe produced. For example, a shell egg processed by the foregoing regimewill have what appears to be a larger yolk than a control. This isthought to be due to egg lipids thinning and running under the prolongedinfluence of the process heat, thereby exerting greater hydraulicpressure against the vitelline membrane which contains the yolk matter.The membrane is comprised of protein and consequently can relax andstretch. This condition does not correct itself when the egg is cooledto ambient or to refrigeration temperatures. Without the control forcomparison, the enlarged yolk may be noticeable only because it will layflatter in a pan than a non-pasteurized egg, for example.

While possibly inconvenient, this consumer noticeable fault is minorwhen compared to the improved food safety of the egg. Nevertheless, moremoderate or optimal process conditions such as pasteurization at 138° F.for about 40 to 46 minutes TPT will typically be employed. This yieldsproducts which are superior in that they are difficult to differentiatefrom controls in any qualitative factor.

As with pasteurized liquid whole eggs, some loss of functionality in anegg processed in accord with the present invention will be noticed by abaker. However, the difference can usually easily be made up by smallincreases in the total amount of egg that is used. This potentialdiminution of functionality is more than offset by the improved foodsafety.

TPT may be reduced by introducing turbulence into the pasteurizationmedium and/or by subjecting the shell eggs to mechanical vibration. Bothof these mechanisms--a turbulent pasteurization medium and theapplication of vibrational energy to the egg--increase the rate oftransfer of heat from the pasteurization medium to the interior of theegg. Thus, while not essential, the utilization of turbulence andvibration can result in more effective treatment regimes. A turbulentpasteurizing medium or vibration of the egg should be used where theadditional benefits of quicker, more effective processing are desirable.

Ultrasonically induced and other forms of vibration including thoseproduced by cavitation may also be employed to advantage in themicroorganism destroying treatment. Such vibration, like that of themechanical variety, promotes the transfer of heat through the shell andthroughout the mass of the egg. This enhances process effectiveness,ensuring more efficient reduction of infectious microorganisms.

Other, advantageous process techniques are deliberate overshooting ofthe selected treatment temperature when the egg is initially heated andthe pulsing or alternating of the treatment temperature between twodifferent levels.

Heating shell eggs and subsequently holding them at selectedtemperatures for an appropriate time to effect pasteurization ispreferably followed by rapid cooling (or quenching) of the treated eggs.This final step ensures that, as they are cooled, the treated eggs passrapidly through that portion of the temperature spectrum favoringbacterial growth. If quick cooling is not employed, any remainingharmful bacteria may multiply and negate some or all of the effects ofthe time-at-temperature treatment, especially if the eggs are allowed toremain for any significant time in a temperature zone favoring microbialgrowth. For this reason, natural cooling of treated eggs to ambientconditions or even cold storage conditions can allow new growth of anyremaining unkilled microorganisms to occur.

Even rapid cooling can have serious drawbacks since microorganisms inthe ambient environment of the treated eggs can recontaminate the eggsurface and be drawn back inside through shell pores by negativepressure generated inside the shell as the egg cools. Therefore, themore rapid the cooling, the cleaner the environment, and the moresterile the cooling environment, the better.

The best possible way to avoid recontamination of the pasteurized eggsby contact with organisms in the ambient environment, by handling, andby other mechanisms is to package the egg in an impervious film or otherpackage prior to cooling. Examples of appropriate films and packagematerials are those fabricated of polyethylenes and polyvinylchlorides.Other acceptable packaging which can be used to prevent recontaminationincludes composite films and readymade, food approved proprietarypackaging such as Cry-O-Vac°, Seal-A-Meal®, and the like.

The egg may be processed in the package and the package asepticallysealed after processing, but before cooling; or the package may besealed prior to pasteurization processing, this being followed bycooling to ambient or a refrigeration temperature. Among the advantagesof processing the egg in packaging is that no recontamination can occurduring steps requiring cooling or handling. The packaging of eggs beforeprocessing, particularly by the dozen or in the other multiples, offersmany other advantages including the ability to use modified atmospheregases such as carbon dioxide, nitrogen, and mixtures as a package fillerto: prevent spoilage; reduce breakage during processing; make handling,the automation of production, and standardization of egg moisture levelseasier; and facilitate the addition and the diffusion into the egg ofprocess aids such as organic acidification agents including citric,lactic, benzoic, and ascorbic acids, to name but a few. Eggs processedin individual packaging may be slipped into more-or-less standard eggcartons while packages in which eggs are processed in multiples may bewrapped or placed in cardboard sleeves to present the packagedappearance commonly expected by the consumer.

Packages may be filled with carbon dioxide, nitrogen, or a carbondioxide/nitrogen mixture before pasteurization or after pasteurizationand before cooling and then sealed. Upon cooling in the sealed package,the gas will be drawn in through the pores in the egg shell and theshell and vitelline membranes to provide a stabilizing, deteriorationinhibiting gas inside the egg.

Storage at acceptable elevated temperature for short durations can beused to effectively pasteurize eggs. Critical parameters for suchstorage pasteurization are temperatures of ca. 131 to 135° F. (±1° F.)for from about 42 minutes to as long as 390 minutes using water--e.g.,in the form of a spray--as a heat transfer medium. Very high humidityair; i.e., air with a relative humidity ≧85% can also be employed as aheat transfer media with the process times then ranging from about 50minutes to 400 minutes. Prepackaging of the eggs before processing ispreferred in this type of pasteurization process due to the manyadvantages heretofore mentioned.

The important objects, features, and advantages of the invention will beapparent to the reader from the foregoing and the appended claims and asthe ensuing detailed description and discussion proceeds in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart depicting the USDA Protracted Whole Egg Standard forpasteurizing liquid whole eggs;

FIG. 2 is a chart showing the minimum conditions mandated by the USDAfor pasteurizing liquid whole eggs and other liquid poultry eggproducts;

FIG. 3 is a pictorial cross-section through a whole, uncooked, poultry,shell egg;

FIGS. 4-8 are charts showing the temperatures reached after TPT's ofzero to 120 minutes at the center of shell eggs processed in water bathswith temperatures of 138, 132, 134, 136, and 140° F.;

FIGS. 9 and 10 are diagrammatic side and plan views, respectively, ofone system which can be employed to pasteurize process poultry shelleggs in small lots in accord with the principles of the presentinvention;

FIG. 11 is a diagrammatic view of one representative device that can beemployed to mechanically vibrate whole shell eggs pasteurizationprocessed in accord with the principles of the present invention inorder to increase the rate of transfer of heat to the centers of theeggs and, in some cases, to scramble the eggs in their shells;

FIG. 12 is a schematic view of a second system for processing wholeshell eggs for improved food safety in accord with the principles of thepresent invention; and

FIGS. 13-17 are schematic views of five other systems for processingwhole shell eggs in accord with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, FIG. 3 depicts a whole, uncooked, poultryegg 20. From outside to inside, egg 20 includes: (1) an egg shell 22;(2) outer membranes which are attached to the inner side of shell 22,include a shell membrane and an egg membrane, and are collectivelyidentified by reference character 24; (3) viscous layers of albumencollectively referred to as the egg white and identified by referencecharacter 26; (4) a liquid yolk 28; and (5) the vitelline membrane 30which is thin and relatively strong and surrounds and envelops egg yolk28. Additional information on the structure of poultry egg components,their functions, and attributes is found in THE AVIAN EGG CHEMISTRY ANDBIOLOGY, Burley et al., John Wiley & Sons, Inc., New York, N.Y., 1989,which is hereby incorporated by reference and which may be referred toby the reader if desired.

Heretofore proposed time and temperature pasteurization techniques forpoultry eggs focus almost exclusively on the destruction of superficialinfections on the outer and inner surfaces 32 and 34 of egg shell 22. Anexception is found in Funk U.S. Pat. No. 2,423,233 which purports todisclose--but does not document--time and temperature pasteurizationprocesses which are capable of destroying infections present in thewhite of a poultry egg. Nothing found to date discloses time andtemperature pasteurization processes capable of destroying infections inthe yolk of a poultry egg, let alone those at the very center 36 of ayolk such as depicted at 28 in FIG. 3. In fact, when applied to a shellegg which is infected throughout its mass or primarily in its yolk, allknown shell egg pasteurization processes are: insufficient to meetminimum effective standards such as those established for liquid eggs;accomplish nothing; or create conditions which are actually conduciveto, and frequently optimal for, the increase of food poisoninginfections already present in the shell egg.

Infections of the shell egg may be commonly found: (1) concentrated ator in close proximity to the egg shell/egg white interface as a resultof migration through the pores of the shell and the outer membranes; (2)indigenous and scattered throughout the mass of the egg; and (3)indigenous but concentrated in the center and other areas of the yolk.Indigenous infections may be a result of: transovarian infection of theyolk, through-the-pore contamination, and generalized infection. Whileit is convenient to think in terms of Salmonella which almost seems tobe symbiotic with poultry and egg products, it is also likely true thateggs serve as rich host media for infectious organisms of all sortsunder some circumstances.

As discussed above, to meet at least the minimum standards ofpasteurization mandated by the USDA for liquid eggs and to retain orenhance the appearance of freshness, functionality, and organolepticproperties, very specific combinations of times and temperatures must beemployed. These time and temperature combinations take into account thesmallest to largest commercial egg sizes; starting temperatures rangingfrom 40 to 70° F.; unpackaged processing without process aids oraugmentation such as by overshooting and flash tempering; and water asthe heat exchange media. The process parameters preferably range from:(a) a minimum TPT of about 34 to 52 minutes at 138.9° F.±0.5° F. to (b)about 75 to 400 minutes at 130.3° F.±0.4° F. Preferred processparameters for shell eggs at a representative 45° F. startingtemperature are:

                  TABLE 2    ______________________________________    Weight (gms)  Temperature (°F.)                              TPT (min)    ______________________________________    40-60         138.5 ± 0.7                              40-46    60-80         138.0 ± 0.5                              42-48    ______________________________________

In many cases, the initial temperature of the eggs being processed willbe below the nominal cold storage temperature of 40° F., above thenominal room temperature of 70° F., or at a level between those twonominal temperatures. For example, cold storage eggs left on a loadingdock in freezing weather may have an initial processing temperaturewhich is less than 40° F. In those cases, minimum, maximum, and optimalprocessing times can be extrapolated from the temperatures set forthabove, derived by the routine testing of appropriately sized samples, orbe derived through a combination of extrapolation and testing steps todetermine the EqT time of the eggs and the TPT required to provide thedesired RPT.

Holding a shell egg under selected time and temperature conditions asspecified above can achieve minimum USDA liquid egg pasteurizationstandards and can effect significant reductions in, if not entirelyeliminate, infections and still yield a consumer acceptable shell egg.

It is entirely practical to process eggs by the novel techniquesdisclosed herein in lots and to employ in the practice of the presentinvention continuous techniques similar to some already in use by theegg industry; e.g., continuous egg washing machines, which can cleanhundreds of thousands of eggs per day. In such applications, it iscommonly impractical to control process temperatures to small fractionsof a degree. Consequently, except for processing steps of very shortdurations, temperatures of less than 139.5° F. are more practicalpasteurization temperatures.

In any event, it is essential that the pasteurization process time andtemperature be such that the shell egg, throughout its mass includingthe center of the yolk and other innermost parts of the egg, reach andbe maintained at a pasteurization temperature for a RPT equal to atleast the minimum USDA required for liquid eggs irrespective of thesize, preprocess temperature, freshness, shell thickness, or othercharacteristic of the egg or the heat transfer medium in which orspecific process by which the egg is processed.

The eggs may be treated or processed in accord with the principles ofthe present invention in any gaseous liquid or fluid, food grade heattransfer medium including air, other gases such as those discussedabove, oil, a glycol, or water.

In those tests described in the examples which follow, counts ofinfections were made with PETRIFILM® aerobic count plates, using theprotocol described in the PETRIFILM® Interpretation Guide, with aMillipore® sampler using the protocol described in the instructions forusing that product, or with an equivalent device and protocol.

The equipment for the tests described in the bulk of the examples isshown diagrammatically in FIGS. 9 and 10. It included a Blue MMAGNAWHIRL precision water bath 38 with controls (not shown) which allowthe temperature of the bath to be adjusted. A batch 40 of eggs to beprocessed was placed in the body of water 41 filling the tank 42 of theBlue M apparatus, typically although not always in batches of 13 arrayedas shown in FIG. 10. Gentle (laminar flow) circulation of the water 41in tank 42 was employed to eliminate temperature gradients and therebyensure that all of the eggs in the body of pasteurization water wereheated in the same, uniform manner.

The temperature at the center of the yolk of that egg 46 in the centerof the batch 40 was measured with a Type K thermocouple 48 at the centerof the yolk. A reference thermocouple 50 placed in the body of water 41in tank 42 was used to measure the temperature of that pasteurizationmedium. Because of the uniformity of the pasteurization conditions, thecenter-of-yolk temperatures of the remaining eggs in a batch 40 wereassumed to be the same as the temperature measured by thermocouple 48.

Thermocouple 48 was installed by puncturing the shell, outer membranes,and vitelline membrane (or yolk sac) of egg 46 with a hypodermic needle.The thermocouple 48 was then introduced with its progress being observedthrough a candling slit, allowing the insertion of the egg to be stoppedprecisely when the temperature sensing tip reached the center of the eggyolk. Epoxy resin was then applied to the shell of the egg to seal thepuncture in the shell and to fix the thermocouple 48 in place.

The center-of-yolk temperature of egg 46 and the bath temperature werecontinuously monitored, using a personal computer 52 running Quick LogPC software supplied by Strawberry Tree of Sunnyvale, Calif. and TegamK,J&T, single input thermometers 54 and 56.

In many of the tests described in the examples, the eggs were inoculatedwith an infectious organism. The number of organisms stated in theexample is the number per gram of egg weight.

EXAMPLE I

Any shell egg subjected to the Funk devitalization process is initiallyat an ambient temperature typically ranging from about 45° to 55° F. Thepreferred Funk TPT's and temperatures (5 to 10 minutes at 138° F. and130° F. for 20 to 40 minutes) cannot provide any RPT in the yolk of aninfected egg as demonstrated by the following tests.

Test 1

Funk preferred TPT/Temperature of 138° F., 5 to 10 Minutes. Method:

Shell eggs were pasteurized at Funk's preferred TPT and temperature. Theeggs had an average size of 60 gms and were at an improbably highpreprocess temperature of 70° F. They were processed in the Blue Mprecision water bath with the water agitated under laminar flowconditions to provide uniform heating (a favorable equivalent of Funk's"rotation"). Results:

After 5 minutes, a yolk center temperature of only about 93° F. wasreached (see FIG. 4). This is nearly the optimal growth temperature formost Salmonella sp. (98.6° F.).

After 10 minutes, the yolk achieved momentarily a temperature of about125° F., still in the temperature range in which microorganisms activelygrow.

Comments

If the yolk of the egg processed in this manner happens to be infectedwith S. enteritidis, for example, such treatment will in effectrepresent exposure of the infected egg to active infection growthconditions (>˜70 to <˜120° F.), including some exposure at optimalgrowth conditions (>˜95 to <˜105° F.) with absolutely no exposure toeffective killing conditions (>˜129 to 160° F. for at least 3.0minutes).

Conclusion

Eggs processed according to Funk's preferred TPT/Temperature conditionscan only result in increased severity of any food poisoning infections,except superficial ones.

Test 2

Funk Preferred TPT/Temperature of 130° F., 20 to 40 Minutes.

Method

Same method as in Test 1 except that the eggs processed in the mostfavorable of all possible Funk TPT/temperatures combinations--130° F.for 40 minutes.

Results

Starting at the very favorable but improbably high starting temperatureof 70° F., the center of the egg yolk reached a temperature of only 130°F. (after ca. 36 minutes). That is, it took 36 minutes to reach EqT andinitiate RPT.

Comments

This leaves a RPT of only four minutes before Funk's mandated maximum of40 minutes TPT is reached. That RPT of 4 minutes at 130° F. is notnearly long enough to pasteurize the egg to a level equivalent to themost minimal USDA liquid egg standard.

Even at a processing temperature of 138° F. an egg acquires an initialtemperature throughout its mass which is effective to destroy infectiousmicroorganisms of about 129 to 130° F. only after 36 to 37 minutes.After an additional x minutes (the total RPT), the average of alltemperatures over the RPT can be compared to the extended chart of FIG.2 to determine if minimal process values have been satisfied. Clearly, atotal RPT of 4 minutes even at 138° F. is not nearly long enough topasteurize the egg to a level equivalent to the minimum USDA liquid eggstandard.

With the center of the egg yolk reaching 130° F. at the 36th minute and132° F. at the 40th minute, additional time at temperature would berequired for the average temperature to achieve a time at temperatureequivalent of the minimum USDA standards shown in the USDA chart.

At least a 50 percent greater RPT of 6 minutes is required at a 138° F.pasteurization temperature to ensure the destruction of infectiousorganisms throughout the mass of the egg. A far longer time would berequired if the temperature at which the egg is heated were only 130° F.

Ignoring Funk's preferred TPT/temperature combinations and sortingthrough a multitude of possible permutations of other possible FunkTPT/temperature combinations leads to the inevitable conclusion that themost efficacious probable selections fail by significant margins toachieve any meaningful RPT with respect to meeting minimum USDA standardrequirements. The many other possible combinations of from 5 to 40minutes at a temperature in the range of 110 to 140° F. in a majority ofcases can only worsen an infectious condition in an egg.

Tests 3-6

The test was repeated, using water bath temperatures of 132° F., 134°F., 136° F., and 140° F. In the first three of these tests the center ofthe egg yolk never reached the 130° F. minimum necessary to achieve anyRPT whatsoever in Funk's maximum 40 minute TPT (see FIGS. 5, 6, 7, and8).

Comments

The sixth--140° F. bath temperature test--confirmed that eggs cannot betime-at-temperature processed at a temperature of 140° F. or higher butmust be processed for the appropriate RPT at a temperature below 140° F.While the egg achieved initial RPT at 21 minutes of TPT, it also becamecooked at a TPT of 25 minutes or after a RPT of only 4 minutes at anaveraged temperature of between 130 and 133° F. at the yolk center. Thewhites of the eggs processed at this temperature were clouded evenbefore the minimum effective EqT of 130° F. was reached, and the eggswere cooked only a few minutes after the minimum 130° F. EqT was reached(see FIG. 8). Clouding and cooking respectively occurred at TPT's of ca.8 and 24 minutes, both well short of the maximum 40 minutes TPT whichthe Funk patent disclosure embraces.

Conversely, the 5 minute TPT taught by Funk to be satisfactory isequally ineffective. In none of the tests (132-140° F., FIGS. 4-8) didthe centers of the egg yolks reach the minimum 130° F. temperaturerequired for microorganism destruction in the Funk-specified 5 minuteTPT.

One can only conclude that Funk does not make obvious to one of ordinaryskill in the art the time and temperature combinations required topasteurize shell eggs to a level required for food safety; i.e., to eventhe minimum level mandated by the USDA for liquid whole eggs.

EXAMPLE II

Two dozen fresh shell eggs at 40° F. (4.4 C.) were placed in a 2-gallon,controlled temperature, water bath preheated to 134.6° F. (57° C.).

Two dozen fresh shell eggs at 40° F. (4.4° C.) were placed in a2-gallon, controlled temperature bath filled with peanut oil. Thetemperature of the bath was preset to 134.6° F. (57° C.).

At 5 minute intervals, eggs were punctured with a stem thermometer whilestill in the bath to determine the temperature at the center of the egg.At 5 minutes, the center-of-yolk temperature of the eggs in both bathsstill averaged only 40° F. (4.4° C.). At 10 minutes, that temperature ofthe eggs from both baths averaged 47° F. (8.33° C.). The 15 minuteaverage for both batches was 67° F. (19.44° C.). At 20 minutes, theaverage temperature was 82° F. (27.78° C.). At 25 minutes, it was 98° F.(36.67° C.). At 30 minutes, the average was 113° F. (44.99° C.). At 35minutes, the average temperature was 121° F. (49.44° C.). At 40 minutes,the average was 129° F. (53.89° C.). At 45 minutes, the averagetemperature was 134° F. (56.67° C.).

The target temperature at the center of the eggs of 129.9° F. (54.4° C.)was achieved at a time between 40 and 45 minutes. The eggs held for thisperiod of time showed no signs of occlusion of the white. Indeed, thewhite had thickened, making the egg appear fresher.

This phenomenon of the egg white thickening without occlusion continueduntil about 1.5 hours had elapsed at which time a very slight butnoticeable occlusion of the white appeared. The appearance of the eggwas very similar to that of a freshly laid egg, which has a somewhatlightly occluded white.

The bunch-up of the white around the yolk and the disappearance of thinrunning egg white continued up to 1.75 hours after which the egg becamemore noticeably occluded.

Eggs which had been held for 1.5 hours at 134.6° F. (57° C.) wereequivalent to shell eggs held at 139° F. (59.4° C.) for 1.25 hours. Theraw eggs were tested by a panel for appearance and were then prepared byfrying, scrambling, and poaching and tested for taste against controls.No significant differences were detected.

EXAMPLE III

Shell eggs for this test were selected for obvious surface filth; i.e.,fecal matter, blood streaks, smudges, feather adherence, and the like.Eighteen medium sized eggs selected from several thousand were rinsed ina 0.005% chlorine water solution. The eggs were immersed in a water bathpreset to 139° F. (59.4° C.). Every 5 minutes, while still in the waterbath, the shell of an egg was punctured and a thermometer inserted intothe center of the yolk. The egg was then removed, the shell was broken,and the egg was dropped into a Petri dish for examination andpreparation of culture samples.

The results after culturing for the indicated number of hours are shownin Table 3.

                  TABLE 3    ______________________________________                              Millipore                              Culture Results    Condition      Temperature                              (microorganisms per cc)    ______________________________________     5 mins          White clear  Yolk/38° F.                                  <50/48   hrs    10 mins          White clear  Yolk/39° F.                                  <100,000/48                                           hrs    15 mins          White clear  Yolk/51° F.                                  0/48     hrs    20 mins          White clear  Yolk/74° F.                                  <9,000/48                                           hrs    25 mins          White clear  Yolk/88° F.                                  <100/48  hrs    30 mins          White clear  Yolk/101° F.                                  <50,000/48                                           hrs    35 mins          White clear  Yolk/117° F.                                  <200,000/48                                           hrs    40 mins          White clear  Yolk/129° F.                                  <50/48   hrs    45 mins          Thicker      Yolk/135° F.                                  <10/48   hrs    50 mins          Thicker      Yolk/139° F.                                  <20/48   hrs    55 mins          Thicker      Yolk/139° F.                                  <40/48   hrs    60 mins          Thicker      Yolk/139 F.                                  <10/48   hrs    65 mins          Thicker      Yolk/139° F.                                  0/48     hrs    70 mins          Thicker      Yolk/139° F.                                  <10/48   hrs    75 mins          Thicker, very                       Yolk/139° F.                                  0/48     hrs          slight occlusion    80 mins          Thicker, slight                       Yolk/139° F.                                  0/48     hrs          occlusion    85 mins          Thicker, slight                       Yolk/139° F.                                  0/48     hrs          occlusion    90 mins          Thicker, occlusion                       Yolk/139° F.                                  0/48     hrs.    ______________________________________

EXAMPLE IV

Medium and large grade eggs stored either at room temperature (70° F.)or at 45° F. for 12 hours were inoculated with Salmonella typhimuriumbacteria (10⁶ /gm) either between the shell and outer membranes (outer)or directly into the yolk (inner).

The inoculated eggs were placed in a water bath operated at differenttimes at 134, 136, and 138° F. (±0.3° F.). Ten eggs representing eachcombination of variables (starting temperature, egg size, andpasteurization process temperature) were removed at two-minute intervalsbeginning after initial heating for 38 minutes and continuing through 50minutes. This represented 38, 40, 42, 44, 46, 48, or 50 minutes of totalheating (TPT). The sampled eggs were cooled to room temperature andanalyzed.

For each combination of variables described above (egg size, egg storagetemperature, heating time, and heating temperature), another 10uninoculated eggs processed at the same temperatures and for the sameTPT's were utilized for functionality evaluation. After heating/cooling,these eggs were cracked open; and yolk/white color, egg whitewhipability, and yolk emulsification capacity were evaluated. Eggs ofthe same size and at the same storage temperature served as controls.

The Salmonella kill results appear in Table 4 below.

                                      TABLE 4    __________________________________________________________________________    Salmonella Reduction (percent)    Egg size:  Medium        Large    Initial egg temp, ° F.:               70° F.                      45° F.                             70° F.                                    45° F.    Inoculation:               outer                  inner                      outer                         inner                             outer                                inner                                    outer                                       inner    __________________________________________________________________________    Pasteurization             --               -- --  -- --  -- --  -- --    temp, 134 ° F.    Heating time, min:             38               43 35  29 18  40 33  25 15             40               46 38  31 20  45 35  29 18             42               52 43  34 21  50 40  31 20             44               55 45  36 24  53 43  35 22             46               64 52  39 27  60 50  37 25             48               73 64  40 30  70 60  39 27             50               87 72  43 31  85 70  41 30    Pasteurization             --               -- --  --     -- --  -- --    temp, 136° F.    Heating time, min:             38               47 37  33 23  45 35  30 20             40               50 40  35 25  47 37  33 23             42               55 46  41 29  51 40  40 26             44               58 49  46 31  55 45  44 29             46               67 58  50 34  63 53  48 30             48               81 72  54 36  77 68  50 35             50               93 80  56 38  90 77  53 37    Pasteurization             --               -- --  --     -- --  -- --    temp, 138° F.    Heating time, min:             38               67 48  65 61  65 45  63 42             40               73 52  70 68  70 50  68 48             42               91 81  87 85  89 80  85 77             44               100                  96  96 93  100                                94  96 90             46               100                  100 100                         100 100                                100 100                                       100             48               100                  100 100                         100 100                                100 100                                       100             50               100                  100 100                         100 100                                100 100                                       100    __________________________________________________________________________

Even in the worst case situation (large egg, 45° F. initial temperature,yolk inoculation), a 100 percent bacterial kill was obtained with 46minutes TPT at 138° F.; and a satisfactory kill was obtained in alltests in which the eggs were processed to levels equivalent to orexceeding the minimum USDA standards for liquid whole eggs.

No egg white separation or coagulation were noted in any of the eggsevaluated in this study. Even the longest heating time (50 min) producedno adverse results. In addition, no changes in egg white and yolk colorwere observed. Likewise, egg white whipability and egg yolk emulsionstability were not significantly different than in the non-heatprocessed controls.

EXAMPLE V

For each test, 12 shell eggs at an initial center of yolk temperature of50±1.5° F. and varying in size from 54 to 67 gms were placed in the BlueM MAGNAWHIRL precision water bath. The eggs were monitored by a TYPE K,hypodermic probe thermocouple coupled to a Tegam K,J&T, single input TCthermometer. The results were as follows:

                  TABLE 5    ______________________________________    Pasteurization Temperature                    130° F.                            134° F.                                     136° F.                                           138° F.    Number of Eggs Tested                    260     200      180   180    Average Size (gms)                    53      60       64    57    Average Time Before EqT (min)                    62      44       40    38.5    Range of Time (min)                    ±1   ±1.5  ±1.5                                           ±1.5    ______________________________________

The size and temperature of an egg entering a pasteurization medium aresignificant determinants of EqT and TPT. As a rule, for highest foodsafety, the lower the temperature at which an egg is held (down to about38° F.), the better. At temperatures below about 45° F., the growthactivity of shell egg infections is very low if not static. Anysignificant holding time before pasteurization at above 55° F. isundesirable since, from that point, the active growth of infectiousorganisms can be substantial. Virtually all shell eggs which are to bepasteurized should be at a temperature below 50° F. Less than 45° F. ispreferred.

EXAMPLE VI

Breakage due to initial process temperature shock can be a significantfactor. Usually, the lower the starting egg temperature, the morefrequent breakage is. Breaking can be reduced by tempering shell eggsbefore they are heated to the pasteurization temperature. Tempering isaccomplished by employing at least one intermediate, rapid incrementalheat exposure step and is described in detail below.

Sixty-four (64) refrigerated fresh eggs (48 hrs old) were inoculatedwith 10⁹ microorganisms per gram of Salmonella typhimurium in distilledwater by shell puncture with a Micropoint 0.3 cc syringe. Sixteen (16)medium and 16 large eggs were punctured and injected with 0.2 cc of theculture immediately beneath the shell and outer membranes. Sixteenmedium and 16 large eggs were similarly inoculated by puncture throughthe vitelline membrane to the proximal center of the yolk as visuallygauged while viewing the egg through the candling aperture. Eachpuncture hole was filled with a dab of hot resin, which was allowed tocool for 5 minutes. The eggs were then divided into two groups of 32,each comprised of 16 54±1 gram and 16 68±1 gram eggs with eight eggs ofeach size being shell inoculated and the other eight being yolkinoculated.

The eggs were placed in separate, precision temperature controlled,water baths, one set at 45° F. and the other at 65° F. After an elapsedtime of 60 minutes, four 54 gram and four 68 gram eggs from each waterbath were punctured by a type K hypodermic thermal probe, and thetemperature at the center of the yolk was taken. As measured at the yolkcenter, all eggs were at a temperature within 1° F. of the bathtemperature; i.e., four eggs were at approximately 45° F. and 4 atapproximately 70° F. Samples taken from puncture points at the innershell and yolk center were cultured. The results were: averageSalmonella for all eggs equalled 10⁸ /gm, the range being from 10⁵ to10⁹ microorganisms per gram.

Inoculated eggs making up the two groups were respectively placed inwater baths operating at 136±0.5° F. and at 138°±0.5° F. After 35minutes of residence time in the bath, a sample of four eggs was removedand cooled in a water bath set at 40° F. for 15 minutes. Each sample wascomposed of 54 gm eggs with initial temperatures of 45 and 65° F. and 68gm eggs with the same initial temperatures.

This sampling procedure was repeated at 2 minute intervals; i.e., after37, 39, 41, 43, 45, 47 and 49 minutes of TPT. All eggs were analyzed forSalmonella.

The remaining 8 eggs were withdrawn and cooled in a water bath at 40° F.These were tested against 8 untreated eggs of comparable age and sizefor visual appearance, whipability, yolk emulsification, and baking(standard sponge cake) equivalency test.

The results of these tests are presented in the following tables.

                  TABLE 6    ______________________________________    Initial temperature = 45° F.    Process Temperature = 136 ± 0.5° F.                       Reduction of Salmonella                       Population (Percent)    Egg Size (gm)               TPT (min)     White   Yolk    ______________________________________    54         35            28      17    54         37            32      20    54         39            34      26    54         41            60      30    54         43            75      65    54         45            83      72    54         47            90      82    54         49            92      84    68         35            29      12    68         37            33      22    68         39            41      24    68         41            59      28    68         43            63      46    68         45            79      69    68         47            85      71    68         49            90      82    ______________________________________

                  TABLE 7    ______________________________________    Initial Temperature = 65° F.    Process Temperature = 136 ± 0.5° F.                       Reduction of Salmonella                       Population (Percent)    Eag Size (gm)               TPT (min)     White   Yolk    ______________________________________    54         35            28      17    54         37            34      23    54         39            35      25    54         41            40      29    54         43            73      61    54         45            81      76    54         47            95      85    54         49            100     92    68         35            27      12    68         37            31      19    68         39            33      24    68         41            59      28    68         43            71      51    68         45            79      71    68         47            93      80    68         49            98      88    ______________________________________

                  TABLE 8    ______________________________________    Initial Temperature = 45° F.    Process Temperature = 138 ± 0.5° F.                       Reduction of Salmonella                       Population (Percent)    Egg Size (gm)               TPT (min)     White   Yolk    ______________________________________    54         35            38      22    54         37            45      26    54         39            51      44    54         41            71      67    54         43            96      89    54         45            100     95    54         47            100     100    54         49            100     100    68         35            31      17    68         37            41      23    68         39            48      38    68         41            57      50    68         43            89      88    68         45            99      97    68         47            100     100    68         49            100     100    ______________________________________

                  TABLE 9    ______________________________________    Initial Temperature = 65° F.    Process Temperature = 138 ± 0.5° F.                       Reduction of Salmonella                       Population (Percent)    Egg Size (gm)               TPT (min)     White   Yolk    ______________________________________    54         35            54      25    54         37            63      31    54         39            88      41    54         41            97      54    54         43            100     90    54         45            100     100    54         47            100     100    54         49            100     100    68         35            31      29    68         37            47      35    68         39            56      48    68         41            80      74    68         43            94      91    68         45            100     100    68         47            100     100    68         49            100     100    ______________________________________

Even in the worst case situation, (large egg, 45° F. initialtemperature, yolk inoculation), a 100 percent kill was obtained with aTPT of 45 minutes at a pasteurization temperature of 138° F., and asatisfactory kill was obtained after a TPT of about 41 minutes.

Very minor cooking was noted in the whites of about 5 to 10 percent ofthe smaller eggs with an initial 65° F. temperature processed for 49minutes at a temperature of 138±0.5° F. No cooking was observed in anyof the other eggs tested. No changes in egg white or yolk color wereobserved. Egg white whip-ability and egg yolk emulsion stability werenot significantly different than in the unprocessed controls. Spongecakes baked in accord with National Egg Board recommendations fromtreated eggs in all four egg size/initial temperature categories wereequivalent to those baked from the controls.

The overall appearance of freshness was equivalent to that of freshlylaid eggs. There was a noticeable enlargement of the yolks of the eggsin the 65° F. starting temperature group processed for more than 45minutes but only when the processed eggs were closely compared to thecontrols. Yolks of eggs processed for TPT's exceeding 45 minutes seemedto rupture more readily than those of the controls when the eggs werecracked onto a hard surface. Additional tests in which treated eggs werechilled for longer periods of time (over 24 hrs at 42° F.) showed thatthis extended chilling restored the rupture resistance of the processedegg yolks to a breakage level about equal to that of normal yolks.

All treated eggs exhibited Haugh values (thickness of white; industrystandard for measuring the freshness of a shell egg) equivalent and insome cases markedly superior to those of controls. Almost 50 percent ofthe eggs processed for 47 minutes (those weighing 54 and 68 gms whetherprocessed from an initial temperature of 45° F. or 65° F.) exhibitedsome opacity in the whites. The observed type of opacity is visuallyindistinguishable from that of eggs which are very fresh or which havebecome partially occluded prior to significant coagulation or loss ofSLP (soluble liquid protein). SLP is a measure of coagulation (see theabove-cited Swartzel et al. patent No. 4,957,759).

Vibration of the eggs being processed by shaking or with ultrasonicenergy or cavitation is another optional technique that can often beemployed to advantage in the processing of eggs according to theprinciples of the present invention. Vibration promotes the transfer ofheat to the inner parts of the egg, making the pasteurization processmore efficient and ensuring an optional kill of any infections that maybe present, irrespective of that part of the egg in which the infectionmay be located.

The advantages of employing vibration were demonstrated in the testsdescribed in the following examples.

EXAMPLE VII

Control: 120 medium sized, 52 gm shell eggs at 70° F. were pasteurizedat 138° F. in the Blue M water bath. Temperatures were taken at yolkcenter with the type K hypodermic thermal probe at intervals during aTPT of 37 minutes.

A Treated: same as control except that the eggs were placed on areciprocating shaker platform located at the bottom of the 138° F. waterbath. The platform was reciprocated at a 1/2 in pitch and at a frequencyof 60 to 75 cycles per minute.

B Treated: 120 medium size eggs at an initial temperature of 70° F. wereprocessed in batches of 12 per test (10 tests) in a Branson Type D,Ultrasonic Precision Water Bath set at power level 4 with the water at atemperature of 138° F.

The yolk center temperatures of the eggs at the indicated samplingintervals are presented in the following table.

                  TABLE 10    ______________________________________            Average    Average   Average            Temperature                       Temperature                                 Temperature            (° F.)                       (° F.)                                 (° F.)            Control    Test A    Test B    ______________________________________     5 minutes              100.0        101.0     101.0    10 minutes              122.4        124.5     123.7    15 minutes              125.0        126.6     127.0    20 minutes              128.6        130.5     131.3    25 minutes              133.0        135.0     135.0    27 minutes              134.0        135.5     136.3    29 minutes              135.0        136.6     137.0    31 minutes              135.5        137.2     137.5    33 minutes              135.7        137.9     137.7    35 minutes              136.2        138.0     138.0    37 minutes              137.0        --        --    ______________________________________

The tabulated results clearly show that the rate of heating of a shellegg can be significantly increased by subjecting the egg to vibration.This translates into a quicker reaching of EqT, with a consequentshortening of TPT and a concomitant reduction in processing costs.

Comparing the EqT of eggs subjected to ultrasonic vibration withcontrols processed identically (except for ultrasonic vibration) at 136°F. for 44 minutes showed that an average five-to-eight percent increasein heat transfer efficiency was obtained at medium power settings of theBranson Ultrasonic Cleaner. The range of improvement in heat transferefficiency ranged from three percent to as high as 15 percent.

Tests of eggs from the same batch and inoculated with Salmonellatyphimurium at a concentration of 10⁸ microorganisms per gram showed anincreased reduction of the infection compared to eggs pasteurized underthe same conditions for the same time; i.e., 138° F. for 41 minutes,both when ultrasonic energy generated at the same settings andmechanical vibration were employed. The average was an approximately 14percent greater reduction in the TPT required for destruction of theinfection at a given pasteurization process temperature (which can alsobe translated into a lower temperature for a given TPT). The increase ininfection reduction ranged from about 5 percent to 20 percent for thesame TPT's at the same process temperatures.

EXAMPLE VIII

One significant discovery arising from the time-at-temperaturepasteurization of shell eggs with mechanical vibration is that shelleggs can be scrambled inside the shell by application of the vibratorytechnique. Tests employed an adjustable, reciprocating flask shaker; anadjustable, orbital test tube mixing pad; and the Branson ultrasonicapparatus. The ultrasonic energy did not produce in-shell-scrambledeggs; the outer membranes of those eggs remained intact. In all testsutilizing mechanical vibration, it was found that shell eggs can bescrambled in the shell over a wide range of frequencies, amplitudes, andprocess times. Heating the eggs markedly reduced the time need formechanical vibration to scramble the eggs in-shell.

The foregoing findings were confirmed by tests in which three dozenshell eggs were pasteurized at 139° F. for 50 minutes in a water bath inthe Blue M apparatus.

After removal from the bath and while still very warm to the touch, theeggs were loaded into an orbital shaker and affixed by elastic retainersto the shaker arms as shown diagrammatically in FIG. 11. The shaker isidentified by reference character 60, the four arms by referencecharacters 62a-d, the eggs by reference characters 64a-d, and theelastic retainers by reference characters 66a-d. The shaker armsoscillated over an adjustable throw or amplitude identified by arc 68about an axis 70. The amplitude was varied over a range of 1/32 in to5/8 in and the frequency over a range of 50 and 500 cps.

Upon opening, about 60 percent of the eggs which had been vibrated for 7to 10 minutes at amplitudes between about 1/4 in and 7/16 in wereprescrambled in the shell. The prescrambled eggs could be brokendirectly into a pan and perfectly scrambled.

Heating eggs subjected to vibration facilitated the transfer of heat tointernal egg particles by producing contact of the heated shell with allparticles inside the egg. This translates into improved pasteurizationefficiencies.

Cold eggs were also scrambled, using the orbital shaker and theoperating conditions described above. There was less uniformity ofscrambling, and there appeared to be some shell membrane tearing.Warming the eggs to a temperature above 130° F. (54.44° C.) alleviatedthose problems.

Eggs processed with ultrasound were not scrambled.

EXAMPLE IX

Several eggs were tested at much higher frequencies and shorteramplitudes, i.e., between about 700 and 800 cps at a 1/64 in to 1/32 inthrow for a total time of about 15 minutes. A very unusual phenomenonoccurred. Upon opening the shell, it was found that the egg had becomealmost entirely one large yolk, there being little or no distinct eggwhite inside the shell. After a few minutes on a flat surface, however,egg white began to slowly reappear from the yolk. Apparently, the whitewas worked through pores in the vitelline membrane by the vibrations.The membrane expanded without breaking to compensate for the muchgreater encompassed volume attributable to the migrated egg white.

EXAMPLE X

It was pointed out above that it is often advantageous in the practiceof the present invention to overshoot the selected pasteurizationprocess temperature in the initial heating of the egg(s) being processedand then allow the temperature to drift down to the selected level. Thisapproach has the advantage of increasing the rate of heat transferthrough the egg to the yolk which, in effect, shortens EqT and,consequently, TPT. High temperature overshooting may require the use ofa heat transfer medium at a temperature which will result in cooking ofthe white before the RPT required for the wanted pasteurizationthroughout the mass of the egg including the yolk center is reached.

Up to a point, the higher the overshoot temperature, the greater therate of heat transfer through the egg. In effect, this results in adesirably reduced EqT. If the egg is placed in water at 145° F., theouter layers will show visible signs of cooking in about 5 to 10minutes, depending on the size of the egg and its original temperature.However, if the egg is removed from the heat transfer media after a fewminutes and before coagulation, the temperature will drop below criticallevels at the surface; and the heat imparted by the initial immersionwill dissipate rapidly into the egg. If the egg is then immersed in apasteurization bath (gas, fluid, or liquid) with a temperature lowerthan the critical temperature producing virtually instant coagulation(about 140° F.), the time required for RPT at the selectedpasteurization temperature may be shortened and the egg pasteurizationprocessed without additional risk of coagulating the yolk. This resultsin a shorter EqT time and a longer RPT for a given TPT and, as a result,more effective destruction of infective organisms than is otherwisepossible.

A typical overshoot temperature ranges from 139-150° F. The overshoottemperature is used for about 2 to 3 minutes and is followed by adecrease to a process temperature in the 130 to 139+° F. range (butbelow 140° F.). The time employed will vary with the size or load of theeggs and the starting temperature of the eggs. The lower thepasteurization temperature selected, the higher the overshoottemperature which can be conveniently used. Higher pasteurizationtemperatures require closer controls and reduced time to prevent visiblecoagulation.

The advantages of employing overshoot (or intermittent pasteurizationwere demonstrated by a representative test in which 12 medium sized eggsat a preprocessing temperature of 55° F. were tempered in water at 132°F. for 3 minutes, removed from the water bath, allowed to dwell for 3minutes in room temperature air, and then introduced into a 138° F.water batch in the Blue M apparatus. The following temperatures weremeasured: non-yolk portion of the tempered egg next to its shell, 131°F.; the middle portion of the white, 112° F.; the white adjacent theyolk, 77° F.; the outer edge of the yolk, 58° F.; the center of theyolk, 56° F.

Thus tempered eggs were also placed in a water bath at a temperature of143° F. (above the coagulation point of egg white albumin), and thewater bath temperature controller was at that time reset to 138° F.

Results

The time required to reach EqT of the eggs started at 143° F. wasshortened by an average of 10 percent with no noticeable diminution inegg quality. This permits processing at preferred pasteurizationtemperatures while reducing TPT by about 5 to 8 percent.

By the time heat transferred through the shells into the outermostlayers of the egg albumin (about 4 to 5 minutes), the temperature of thepasteurization medium dropped to a baseline temperature of 138° F. Inthis short period of time, not enough heat can transfer through theshell and outer membrane to coagulate the outer layers of albumin. Atthe same time and as discussed above, the faster rate of heat transferobtained by employing the higher, initial, overshoot temperaturedecreases EqT and, consequently, TPT.

Much higher temperatures can be used to reduce EqT; but requirements forcloser process parameter controls to prevent increased thermal shockbreakage and risks of coagulation will be limiting factors. Theselimiting factors depend upon the quantity of the product pasteurized andthe particular conditions employed for pasteurization.

While the preferred "overshoot" temperature will typically be between139° F. and 150° F., this temperature can range up to about 170° F. Theprocess parameter tolerances at this point, however, are so close thatthese higher overshoot temperatures, for all practical purposes, becomemore or less the same as those required the flash tempering techniquedescribed hereinafter.

EXAMPLE XI

Another technique that can be employed to advantage in the practice ofthe present invention is to pulse the pasteurization processtemperature; i.e., cycle that temperature between low and high levels.This is beneficial because pasteurization temperatures high enough tootherwise cause coagulation can be employed if alternated periodicallywith less critical and lower but effective pasteurization temperatures.This approach enhances heat transfer to the egg center withoutcoagulation of the white. This reduces TPT as a result of a reduced EqTtime.

Preferred intermittent/periodic temperatures of the pasteurizationmedium are between about 130 and 138° F. on the low side and about 139.5and 145° F. on the high side. These temperatures are within a practicalrange for pulsing. Eggs being pasteurized can effectively bealternatively treated at a baseline pasteurization temperature of 130°F. or higher and a pulse temperature of 139° F. to 145° F. or evenhigher, provided that the time of exposure at the higher temperature islimited to a time shorter than that which will cause coagulation of thewhite at the selected high side or pulse temperature. However, closercontrol over the process parameters must be exercised when using higherpulse temperatures.

As an alternative to pulsing in the same media, eggs may be transferredbetween baseline temperature heat transfer media and higher pulsetemperature transfer media. Also possible are combinations of techniqueswhich employ one or more high side pulse and baseline temperatures andone or more pasteurization media to effect optimal pasteurization whileworking below critical coagulation times and temperatures and providingthe most efficient EqT.

To demonstrate the efficacy of the just-described pulsing techniques, 60gram eggs were heated at 145° F. for 2 minutes. The eggs were then heldat ambient temperature for a dwell time of 2 minutes. This was followedby heating the eggs at 140° F. for 2 minutes and then heating them at130° F. for 38 minutes.

EqT was reached after 35 minutes. This was 4 minutes faster thancontrols heated at 138° F. This represents an 11 percent decrease inEqT.

EXAMPLE XII

The percentage of eggs damaged by cracking increases as the differentialbetween the initial and pasteurization process temperatures increases.That is, the more severe the temperature differential, the more eggsthat will crack. This number can become substantial when shell eggs aresubjected to the temperatures at the upper end of the usefulpasteurization temperature range. To overcome this serious problem, theshell eggs are preferably raised to process temperatures in at least oneand preferably two or more steps. This process of heating eggs fromtheir initial temperature to the pasteurization temperature in stages toreduce breakage and for other purposes is referred to herein astempering.

Tempering is typically accomplished by holding the eggs in air,preferably in a sanitary enclosure at one or more intermediatetemperatures in the range of 65 to 131° F. for a total period of 10minutes to 24 hours with the particular time(s) and temperature(s)depending on such factors as: the temperature conditions under which theeggs were heretofore held; the size of the eggs; the baselinepasteurization temperature to be used; and whether or not basic processaids such as turbulence, vibration, and/or heat transfer promotingpulsing treatments are to be used.

While not preferred, the minimum tempering temperature can besubstantially lower than 130° F. Particularly when temperingtemperatures below 130° F. are used, the tempering time should be nomore than is required to reduce breakage when the egg is subsequentlysubjected to primary pasteurization because <130° F. temperaturespromote the growth of Salmonella and other dangerous microorganisms.

Tempering quickly to prevent any significant growth of infectionsincluding those superficially present at the inner shell surface orthose at the center of the yolk can be accomplished by flash tempering,which consists of first exposing the shell egg for a brief period oftime to a higher temperature than could be employed if the eggs wereexposed to it for an appreciable length of time.

The temperature for flash tempering can be considerably higher than 212°F.; and such temperatures can be reached by exposing the eggs to steamor an open flame, for example. Unless care is exercised, however, theuse of these super high flash tempering temperatures can result inscorched or "off" odors and/or flavors in the egg. Consequently, thetime of exposure for the temperature selected should be no more than isabsolutely necessary to reduce breakage during processing to avoidimparting any "off" odor or flavor to the egg.

In all cases where tempering is utilized, the dwell or post-temperingtime before entry into primary pasteurization should be of the minimumduration required for the tempering heat imparted to the egg to functionto reduce subsequent breakage. This breakage reducing function may occurduring tempering and also subsequently during the dwell orpost-tempering period and during pasteurization. The total of temperingand post-tempering or dwell times is preferably from about 0.5 minutesat the highest temperatures (ca. 212° F. to steam and open flametemperatures) to 40 minutes.

Tempering at more modest temperatures (134.5 to 138.5° F.) is preferablyaccomplished by heating the eggs being processed in one or more stageswith the eggs being treated in the last stage at a maximum temperatureof 138.5° F. for about 1 minute with a minimum dwell time afterwards ofabout 3 minutes. The total time (heating and dwell) is in the range of 1to 15 minutes. Most generally preferred for a wide variety of processingapplications are tempering temperatures in the range of 130 to 131F. fortotal times of 5 to 50 minutes with 5 to 10 minutes being preferred.

The following table gives preferred pasteurization process parameters(times at temperatures for eggs flash tempered by heating them at arepresentative 146° F. for 2 minutes, this being followed by a dwell atroom temperature of 5 minutes).

                  TABLE 11    ______________________________________    Shell Eggs at 73° F.    Weight       Temperature (°F.)                             TPT (min)    ______________________________________    40-60        138.5 ± 0.7                             35-43    60-80        138.0 ± 0.5                             36-45    ______________________________________

Preferred process conditions for eggs representatively tempered at 125°F. for 2-3 minutes with a 3-5 minute dwell appear in Table 12.

                  TABLE 12    ______________________________________    Shell Eggs at 68° F.    Weight       Temperature (°F.)                             TPT (min)    ______________________________________    40-60        138.5 ± 0.7                             37-45    60-80        138.0 ± 0.5                             38-47    ______________________________________

Tempering as usually accomplished in 5 to 10 minute steps may typicallyadd about 1 to 5 minutes to TPT. Tempering and/or prepackaging and/orcoating steps employed to overcome cracking may significantly increasethe overall process time, especially in applications employing moresevere treatment regimes in the range of from about 135° F. to about140° F.

If accomplished within the specified parameters, tempering does notnecessarily cause any significant increase in TPT or increase ininfections but can significantly reduce EqT and cracking of shells andotherwise contribute to the overall effectiveness of the pasteurizationprocess.

Tempering times will in general be inversely proportional to thetempering temperatures that are employed. That is, the higher temperingtemperatures will be employed for the shorter indicated periods of timeand vice versa. This avoids coagulation, thermal shock induced crackingof egg shells, and other problems which might otherwise occur.

The following representative tests employed tempering in pasteurizingeggs in accord with the principles of the present invention.

Control: 36 medium sized eggs at an initial temperature of 65° F. weredivided into four batches of nine each. The batches were processedseparately and introduced directly into a water pasteurization bathtemperature regulated with a controller preset at 138° F. The eggs wereheld in the pasteurization bath for 20 minutes TPT.

The eggs were removed from the bath at the end of the 20 minute periodand examined for cracks.

Results

Batch 1: Broken eggs=2

Batch 2: Broken eggs=0

Batch 3: Broken eggs=1

Batch 4: Broken eggs=1

A Tempered eggs: 36 medium sized eggs at an initial temperature of 65°F. were divided into four batches of nine each. The batches wereprocessed separately in a water bath regulated by a temperaturecontroller set at 130° F. for 5 minutes and then transferred to a waterpasteurization bath at 138° F. for 15 minutes TPT.

Results

Batch 1: Broken eggs=0

Batch 2: Broken eggs=1

Batch 3: Broken eggs=0

Batch 4: Broken eggs=0

B Tempered Eggs: 36 medium sized eggs at an initial temperature of 65°F. were divided into batches of nine eggs, and the four batches wereprocessed separately in an air box 12 in×10 in×24 in. Air preheated to80° F. was circulated through the box at a rate of 15 cfm for 15 minutesto temper the eggs. Each batch of eggs was then removed from the box andtransferred to the 138° F. water pasteurization bath for 15 minutes TPT.

Results

Batch 1: Broken eggs=0

Batch 2: Broken eggs=0

Batch 3: Broken eggs=0

Batch 4: Broken eggs=0

The reduction in thermal shock cracking afforded by tempering as well asan increased thermal tolerance can be obtained by wrapping, bagging,coating, or otherwise encapsulating the eggs being treated before theyare introduced into the pasteurization medium.

The application of these techniques to time-at-temperature eggpasteurization as disclosed herein is illustrated in the followingexamples.

EXAMPLE XIII

Thirty-six (36) medium sized eggs at an initial temperature of 65° F.were individually tightly wrapped in a Saran® wrap film commonly usedfor wrapping meat and divided into four batches. The four batches ofwrapped eggs were pasteurization processed separately in the 138° F.water pasteurization bath for 20 minutes TPT.

Results

Batch 1: Broken eggs=0

Batch 2: Broken eggs=0

Batch 3: Broken eggs=0

Batch 4: Broken eggs=1

EXAMPLE XIV

Thirty-six (36) medium sized eggs at an initial temperature of 65° F.were divided into four batches of nine and individually sealed inresealable 5 in×6 in Zip Loc® sandwich bags. The four batches of baggedeggs were separately processed in the 138° F. water pasteurization bathfor 20 minutes TPT.

Results

Batch 1: Broken eggs=0

Batch 2: Broken eggs=1

Batch 3: Broken eggs=0

Batch 4: Broken eggs=0

EXAMPLE XV

Thirty-six (36) medium sized eggs at an initial temperature of 65° F.were divided into four nine-egg batches and individually sealed byspraying the shells with a clear acrylic spray (Krylon® 12 ouncespray-on acrylic coating) The coatings were air dried at 70° F., and thecoated eggs were then immersed in the 138° F. water pasteurization bathfor 20 minutes TPT.

Results

Batch 1: Broken eggs=0

Batch 2: Broken eggs=1

Batch 3: Broken eggs=0

Batch 4: Broken eggs=1

Of considerable importance in the practice of the present invention isthe handling and packaging or treatment of the processed egg(s) in amanner which will keep the eggs from being recontaminated with harmfulorganisms. Recontamination can be avoided by packaging the eggsimmediately before pasteurization or immediately after pasteurizationand before cooling or exposure to eliminate potential contamination byhandling or contact with the ambient environment or non-sterilesurfaces.

A preferred technique which can be employed involves: (a) individuallyprepackaging the eggs in a polymeric film formed separately around eachegg, (b) sealing the packages, and then (c) pasteurizing the eggs inaccord with the principles of the present invention.

This approach has the advantages of: reductions in handling and theabove-described thermal shock breakage, elimination of recontamination,and easier control over the process since eggs may be pasteurizedcontinuously on a packed belt line and the individual egg packages thencut apart or otherwise separated. Once sealed in film, the egg does notneed to be pasteurized or handled in an aseptic environment. Also, thiskeeps processing aids such as shell treatment agents from coming offduring processing.

Alternative techniques that can be utilized include sealed packaging inCry-O-Vac® polymers and processing before or after sealing (preferablybefore).

Spoilage preventing inert gases such as carbon dioxide and nitrogen maybe substituted for the air in the packages or added to the eggs byinfusion or the use of negative and/or positive pressures as describedin above-cited parent application Ser. No. 746,940. The packaging may besterilized before use to eliminate any harmful microorganisms present onthe packaging.

The following examples describe in detail representative applications ofa packaging technique as just described in the pasteurization of eggs bythe principles elucidated herein.

EXAMPLE XVI

Eight (8) 60 gm eggs tempered at 140° F. for 5 minutes in circulatingair were removed from the tempering unit and immediately placed in a 500ml beaker filled with CO₂ at 32° F. for 2 minutes. The eggs were removedfrom the beaker and placed in 4 in×4 in Seal-A-Meal® bags, which wereimmediately sealed. The eggs were in-bag pasteurized at 138° F. in awater bath and examined after 40 minutes at 5-minute intervals. The eggsshowed no significant occlusion after pasteurization for 75 minutes.

Controls were all occluded after 68 minutes. This indicates that the COtaken up in the eggs produced an at least 10% increase in heattolerance. This is important in circumstances requiring that the egg beheated at a maximum or near maximum permissible temperature for themaximum length of time--for example, if heavy or widespreadcontamination throughout the mass of the egg with an infection issuspected.

The test was repeated at an otherwise unacceptably high 140° F.pasteurization temperature with the eggs being cracked every 2 minutesafter 6 minutes pasteurization elapsed. CO₂ treated eggs showed littleor no occlusion until after 18-20 minutes of pasteurization. Controlsshowed signs of occlusion after 12-14 minutes.

EXAMPLE XVII

Thirty-six (36) eggs inoculated through the shell with Salmonellatyphimurium (10⁹ /gm) were divided into four nine-egg batches and placedindividually in 4 in×4 in Seal-A-Meal® bags to which 6 gms each of dryice (frozen CO₂) had just been added. The bags were sealed; and eachbatch of bagged eggs was separately processed in the 138° F. waterpasteurization bath for 40 minutes TPT. Four eggs were then removed fromthe pasteurization bath in each run and analyzed.

Results

    ______________________________________              Average Reduction              in Bacteria (percent)    ______________________________________    Batch 1:    ˜70    Batch 2:    ˜80    Batch 3:    ˜60    Batch 4:    ˜70    ______________________________________

The remaining eggs in each bath were processed an additional 2 minutes,removed from the bath, and analyzed.

Results

    ______________________________________              Average Reduction              in Bacteria (percent)    ______________________________________    Batch 1:     ˜100    Batch 2:    ˜80    Batch 3:    ˜90    Batch 4:    ˜90    ______________________________________

As a consequence of adding CO₂ to the bags, it was possible topasteurize the eggs for longer periods or at slightly highertemperatures with delayed occlusion (cooking). Both approaches permitbetter kills of infections.

EXAMPLE XVIII

Mild, safely consumable acids can also be used to increase theresistance of eggs to occlusion or coagulation of the whites, to reducethe loss of functionality, and to reduce other forms of degradationduring time at temperature pasteurization.

This aspect of the invention is illustrated by the following tests:

Control

Thirty-six (36) medium sized eggs were each inoculated through the shellwith 0.05 mls distilled water carrying a Salmonella typhimurium cultureat a rate of 10⁹ /gm and divided into four batches of nine eggs each.The four batches were separately processed in a 138° F. waterpasteurization bath for 40 minutes. Four eggs of each batch were removedfrom the bath and analyzed.

Results

    ______________________________________              Average Reduction              in Bacteria (percent)    ______________________________________    Batch 1:    ˜60    Batch 2:    ˜60    Batch 3:    ˜60    Batch 4:    ˜70    ______________________________________

The remaining eggs were processed an additional 2 minutes, and thebacteria kill was measured in the manner just described:

Results

    ______________________________________              Average Reduction              in Bacteria (percent)    ______________________________________    Batch 1:    ˜70    Batch 2:    ˜70    Batch 3:    ˜80    Batch 4:    ˜70    ______________________________________

Acid processed: The eggs in four nine-egg batches were inoculatedthrough the shell with Salmonella typhimurium (10⁹ microorganisms pergram) in the same manner as the controls. The four batches of inoculatedeggs were separately pasteurization processed in the 138° F. water bathto which 0.2% volume percent of citric acid had been added for 40minutes. Four eggs were removed from each batch, and the bacteria killwas measured.

Results

    ______________________________________              Average Reduction              in Bacteria (percent)    ______________________________________    Batch 1:    ˜60    Batch 2:    ˜80    Batch 3:    ˜70    Batch 4:    ˜70    ______________________________________

The remaining eggs of each batch were processed an additional 2 minutesand the bacteria kill measured.

Results

    ______________________________________              Average Reduction              in Bacteria (percent)    ______________________________________    Batch 1:    ˜90    Batch 2:    ˜80    Batch 3:    ˜90    Batch 4:    ˜70    ______________________________________

The increased level of bacterial kill is significant, especially in thecase of the eggs pasteurized for the additional 2 minutes.

Citric acid may be used for the purposes just described inconcentrations ranging from 0.05 to 0.5 percent based on the volume ofthe bath. Other acids which can be employed for the purposes justdescribed include the above-mentioned ascorbic, benzoic, and lactic.

As discussed in detail in the working examples and elsewhere above,processes employing the principles of the present invention are designedto make shell poultry eggs safer to eat by destroying harmful organismssuperficially resident on the outer surface of the shell and throughoutthe shell and interior of the egg without impairing the functionality ofthe egg or altering its organoleptic properties by holding the shelleggs under time/temperature conditions which will destroy harmfulbacteria on and inside the egg shells.

One system in which a process of this character can be carried out isillustrated in FIG. 12 and identified by reference character 71. Thatsystem includes a holding vessel or pasteurization tank 72, anoptionally employed pore sealing unit 74, a heat exchanger 76, and apackaging unit 78.

As is discussed elsewhere in this specification, the initial step intreating whole eggs in a system like that identified by referencecharacter 71 is to clean and, typically, disinfect the outer surfaces ofthe shell eggs.

The cleaned eggs are transferred to tank 72 where they are held in wateror another pasteurization medium at the temperature and for the timeselected to reduce any infection located anywhere in the mass of theeggs to a level at least equivalent to that obtained by pasteurizingliquid whole eggs to USDA minimum or protracted standards.

Thereafter, the treated shell eggs can be transferred to heat exchanger76 to rapidly reduce their temperature to a level which is below that atwhich growth of any remaining viable bacteria might be a problem andappropriate for packaging. Then, the now cooler eggs are transferred topackaging unit 78 where they are placed in cartons or other containers.

Optionally, the pores and the shells of the treated eggs can be treatedwith palm stearine or other sealing agent before they are packaged inunit 78. This keeps infectious microorganisms as well asoxygen-containing and other unwanted gases from contaminating thepasteurized egg by penetrating through the pores in the egg shells tothe interior of the egg, thereby reducing degradation, preserving foodsafety, and improving the keeping quality of the treated egg.

It was also pointed out above that the keeping quality and food safetyof eggs treated in the manner just described can often be even furtherimproved by evacuating indigenous gases from the interior of the eggshell and replacing the evacuated gases with inert gases before thepores of the egg shell are sealed. A system for carrying out thisprocess is illustrated in FIG. 13 and identified by reference character80.

That system includes pasteurization vessel 72; vacuum vessel 82;packaging unit of 85; pressure vessel 84; sources 86, 88, and 90 ofcarbon dioxide, sterile air, and nitrogen; pore sealing unit 74(optional); heat exchanger 76; and packaging unit 78.

Cleaned and treated eggs are transferred from the tank 72 in which theyare pasteurized to vacuum tank 82. Here, they are held under negativepressure for a period long enough to draw unwanted, indigenous gasesfrom the interior of the egg through the pores in its shell. Of concernare those gases such as oxygen that might cause unwanted chemicalreactions; e.g., those that produce spoilage.

From vacuum unit 82, the shell eggs are transferred, still under anegative pressure, to pressure vessel 84. Sterile gas is introduced intothe vessel from one or more of the sources 86 . . . 90 under pressure;and the eggs are held in this pressurized environment for a period longenough for the selected gas or mixture of gases to infuse through thepores in the egg shell and fill the interstices in those parts of theegg within the shell.

Thereafter, the treated shell eggs may be cooled in heat exchanger 76and packaged in unit 78. Alternatively, the pores in the egg shells mayfirst be sealed in unit 74 to prevent unwanted exchanges between gasinfused into the eggs through the pores in their shells and gases in thesurrounding environs.

Also, in using system 80, the pasteurized eggs may be packaged beforethey are cooled in order to decrease the chances of recontaminationbefore the eggs are cooled. In this case packaging unit 85 is employed,and unit 74 is deactivated. The package may be filled with anatmosphere-modifying gas of the character and for the purposes discussedabove in pressure vessel 84.

Referring still to the drawing, FIG. 14 discloses another "basic" system94 for processing whole shell eggs which includes pasteurization unit 72and cooling unit 78 and, in addition: a shell egg cleaning unit 96, apackaging unit 98, and a storage unit 100 for the packaged eggs.Cleaning unit 96 is conventional and is employed to superficially cleanthe exteriors of the eggs being processed before they are introducedinto pasteurization unit 72.

Packaging unit 98 is also conventional. Here, the eggs are placed incartons or other packages including those designed to hold only a singleegg.

The term storage unit is employed generically. This may be, at varioustimes, and even for the same eggs, a refrigerated warehouse or truck orthe cooler at a retail outlet.

The whole shell egg processing system 104 depicted in FIG. 15 differsfrom the processing system 94 just described primarily by the additionof a tempering unit 106; a post-pasteurization unit 108; and,optionally, a source 110 of an inert gas such as carbon dioxide,nitrogen, or a mixture of the foregoing.

Tempering unit 106 is used vide EXAMPLE XII above and elsewhere in thisspecification to reduce breakage of the eggs being processed, atechnique which is particularly useful when the differential between theinitial egg temperature and the pasteurization process temperature islarge and the risk of breakage is accordingly high. Post-pasteurizationunit 108 is employed to treat the eggs to prevent recontamination bysealing the pores of the egg shells as discussed above or by packagingthe eggs. If the latter technique is adopted, unit 110 may optionally beemployed to fill the packages with an atmosphere modifying gas of thecharacter and for the purposes discussed above.

Depicted in FIG. 16 is a shell egg processing system 112 which differsfrom the FIG. 14 system 94 primarily by the addition of an egg packagingunit 114, an optional inert gas source 116, and a package filling andsealing unit 118.

Packaging unit 114 is employed vide examples XIII-XVII and for thepurposes described in those examples and elsewhere in the specificationto package the eggs cleaned in unit 96 before they are pasteurized. Aninert gas from source 116 may optionally be employed to fill thepackages before they are sealed and transferred to pasteurization unit72. Alternatively, as indicated by reference character 118, the packagedeggs may be optionally filled with a sterile inert gas and sealedimmediately after they are pasteurized and before they are transferredto cooling unit 78.

As discussed above, it is possible to significantly shorten the timerequired to reach EqT in processing eggs for improved safety in accordwith the principles of the present invention by: first heating the eggsto a temperature above that at which they can be heated for a timeequivalent or exceeding the minimum mandated by the USDA for liquidwhole eggs, then holding the eggs for a dwell period in which the heatsoaks into the eggs, and then pasteurizing the eggs at the selectedtemperature in the range specified above. A unit for processing wholeshell eggs in the manner just described is depicted in FIG. 17 andidentified by reference character 122. That system differs from thebasic system illustrated in FIG. 14 primarily by the interposition of anovershoot unit 124 between shell egg cleaning unit 96 and pasteurizationunit 72. The medium in which the eggs are heated in overshoot unit 124may be any of those indicated above to be suitable for use inpasteurization unit 72.

The invention may be embodied in many forms without departing from thespirit or essential characteristics of the invention. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription; and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A process for pasteurizing chicken shell eggs,comprising:(1) heating a liquid process medium to a selected temperaturein a range of 130° F. to less than 140° F. and maintaining that selectedtemperature of the liquid process medium; (2) placing the eggs in theliquid process medium maintained at the selected temperature andallowing the eggs to remain therein for a dwell time sufficient thatevery locus throughout each of the eggs has reached temperatureequilibrium with the selected temperature of the liquid process medium;and (3) thereafter allowing the eggs to further remain in the liquidprocess medium maintained at the selected temperature for a minimum timecorresponding to a straight line graph of the log of time versustemperature where a terminus of the straight line is at about 130° F.and 50 minutes and another terminus of the straight line is at about139.5° F. and 4.50 minutes.
 2. The process of claim 1, wherein the eggsare tempered prior to being placed in the liquid process medium suchthat all of the eggs placed in the liquid process medium are at a sametemperature.
 3. The process of claim 1, wherein turbulence is introducedinto the liquid process medium.
 4. The process of claim 1, wherein,prior to step (2), the eggs are first placed into and withdrawn from aseparate liquid process medium heated to a higher temperature than theselected temperature, but for a period of time insufficient to causecoagulation of the eggs so as to shorten the dwell time required by step(2).
 5. The process of claim 4, wherein the higher temperature is in arange of 139° F. to 1500° F.